An inhibin -subunit cDNA sequence from the Australian brushtail possum (Trichosurus vulpecula) has been identified and analysed. The cDNA includes an open reading frame encoding a predicted precursor protein of 361 amino acids. The predicted protein sequence includes four possible proteolytic cleavage sites, 12 evolutionarily conserved cysteine residues and three potential N-linked glycosylation sites. The mature -subunit is the carboxyl terminal fragment ( C) consisting of 131 amino acids. The full-length precursor protein shows a mean identity with eutherian homologues of 69·8%. The homology is not evenly distributed, with the putative C fragment showing the highest level (79·7%). Using Northern hybridisation, an -subunit transcript of approximately 1·6 kb was detected in adult possum ovary. Using in situ hybridisation and immunocytochemistry, inhibin -subunit was localised exclusively to the granulosa cell layers of follicles. Hybridisation and immunostaining for the inhibin -subunit were first observed in granulosa cells of primary follicles and the expression continued throughout all stages of follicular growth. Inhibin -subunit mRNA and protein were also detected in cells of the corpus luteum. In summary, results indicate considerable conservation of the structure and possible function of the inhibin -subunit protein since the divergence of the marsupial and eutherian mammalian lineages. The expression data suggest that, in the adult possum, inhibin may have a role in ovarian follicular growth from the primary stage of development.

A cDNA sequence from the gonadotrophin -subunit mRNA of Australian brushtail possum (Trichosurus vulpecula) has been determined and analysed. Comparison with seven eutherian mammalian gonadotrophin -subunit gene sequences revealed an average of 82·6% homology between the coding region nucleotide sequences and 88·8% identity between the predicted amino acid sequences. The predicted possum gonadotrophin -subunit protein has ten evolutionarily conserved cysteine residues, two potential N-linked glycosylation sites and a putative enzyme recognition sequence which it has been suggested is required for sulphation of carbohydrate moieties. Comparison of the possum gonadotrophin -subunit 3 untranslated region (UTR) sequence with the 3 UTRs of eutherian -subunit transcripts revealed sequence homology. In particular, an 18 nucleotide imperfect palindromic sequence present in the possum 3 UTR, with the potential to form a hairpin loop, was found to be evolutionarily conserved and present in five out of seven eutherian -subunit 3 UTR sequences. In situ hybridization localized the transcripts to a sub-population of anterior pituitary cells presumed to be gonadotrophs and thyrotrophs. In summary, these results indicate considerable conservation of the structure and function of the gonadotrophin -subunit protein since the divergence of the marsupial and eutherian mammalian lineages.